FR2488346A1 - Single-stage centrifugal pump for liq - has outlet cross=section limiting specific speed to maximum of ten - Google Patents

Abstract

The single-stage centrifugal pump handling liquid has a vaned impeller running in a body with inlet and outlet. The outlet cross-section (22) is limited so that the specific speed of the pump is equal to a max. of 10. The body (2) and the impeller (9) can be castings, and the passages (43) between the impeller vanes can be enclosed between flanges at right angles to the shaft (3), and integral with the impeller. The width of these passages in the axial direction can be greater than 1/40th of the impeller diameter. The outlet passage (22) can be of circular cross- section, and formed in a bush (21) accommodated in a mounting (19) in the pump body.

Description

 The invention relates to a centrifugal pump for liquids with a single stage.

 A pump of this kind comprises a body with an inlet port and an outlet port which houses a paddle wheel defining between them channels of shapes and dimensions such that the rotation of this wheel causes, by the centrifugal force generated, the circulation of '' a liquid from the inlet to the outlet.

It is recalled that the characteristics and performances of such a pump are generally represented by a parameter 5, called specific speed, which is defined by the following formula:
Q112 nnsn "H3 / 4
In this formula n is the speed of rotation of the wheel expressed in revolutions per minute, Q is the output flow expressed in cubic meters per second and H is a height of liquid expressed in meters representing the output pressure.

 It has already been proposed, in order to widen the possibilities of using these pumps, in particular towards low flow rates and high pressures, that is to say towards low specific speeds n5, to have downstream of the outlet orifice a valve for reducing the flow and increasing the pressure. But a valve increases the cost of the installation, causes excessive energy consumption for the pump, and, for low flow rates, deteriorates quickly and generates an annoying noise.

 To obtain low flow rates Q and significant heights H, it is also possible to give a large diameter to the impeller and a small passage width - measured parallel to the axis of rotation of the impeller - of the liquid in the pump, because the outlet pressure is a direct function of the diameter of the wheel and, similarly, the liquid flow rate is a direct function of the passage width.

 However, the latter solution, which is satisfactory for energy consumption and reliability, is however too costly for low specific speeds, at most equal to around 10. Indeed, for these specific speed values, the pump should be conformed so that the ratio between the width of passage of the liquid and the diameter of the impeller is less than 1/40 and it is not possible, with current techniques known, to manufacture in one piece by foundry wheels having a passage width / diameter ratio as low and having, as is desirable, channels closed by walls or flanges perpendicular to the axis of rotation.

 It is however possible to manufacture two-piece castings of such wheels. But in this case, the cost would be too high.

 It would also be possible to manufacture in a single piece by foundry wheels having the dimensional characteristics above provided that the channels are open on one, or both, side (s); but in this case the operating characteristics of the pump would be deteriorated.

 In addition, with a small passage width, the effect of the friction of the liquid against the walls, due to the inevitable irregularities of the latter, causes a reduction in the efficiency of the pump. In addition, these irregularities being random, pumps of identical dimensions, even manufactured simultaneously, would not have the same operating characteristics.

 Small specific speeds can also be obtained by having several pumps in series, each having a wheel with closed channels, and manufactured in one piece by foundry. But the cost would still be too high.

 It is also possible to envisage the manufacture by molding of plastic material or by stamping of metal sheet of such wheels with reduced width / diameter ratio under satisfactory economic conditions. However, the applications of such pumps would be limited because they would not allow corrosive or abrasive liquids to circulate at high pressures and extreme temperatures, while a pump manufactured by foundry in stainless steel or not, or in cast iron, allows the otherwise the circulation of corrosive or abrasive liquids at high pressures and high temperatures.

 The invention therefore aims to provide a centrifugal pump with a specific speed at most equal to 10 which can be manufactured economically by foundry.

 The pump according to the invention is characterized in that it has a section outlet channel, in particular of circular shape, limited so that the specific speed ns of the pump is at most equal to approximately 10.

 The limitation of the flow rate is thus obtained by acting on the outlet channel, that is to say in a particularly simple, economical and reliable manner. In addition, the wheel can be dimensioned so that it can be easily fabricated by a single piece foundry even if its channels are closed.

 It is therefore possible to manufacture a pump with a specific speed at most equal to 10 under satisfactory conditions of reliability and cost price.

 In the preferred embodiment of the invention, the pump body includes a housing for a removable socket in which the outlet channel is formed. In this way, the characteristics of the pump can be modified at will by modifying the section of the outlet channel formed in the socket.

 In an embodiment intended for pumps for the circulation of liquids containing abrasive particles, the sleeve is in one.

material with high abrasion resistance.

- Other characteristics of the invention will appear with the description of some of its embodiments, this being carried out with reference to the attached drawings in which:
- Figure 1 is a schematic view, in section perpendicular to the axis of rotation, of a pump according to the invention
- Figure 2 is a section along line 2-2 of Figure 1
- Figure 3 shows, in section perpendicular to the axis of rotation, the outlet of the pump shown in Figure 1 and a connection means to a tube;
- Figure 4 is a view similar to Figure 3 for a variant;
- Figure 5 is also a view similar to that of Figure 3 but for another variant;
- Figure 6 is an enlarged view of part of the pump shown in Figure 1;
- Figures 7, 8 and 9 are diagrams illustrating the operating characteristics of the pump according to the invention;
- Figure 10 shows a wheel whose channels delimited by the blades are open on one side;
- Figure 11 is a view similar to that of Figure 10 but for a impeller pump whose channels delimited by the blades are open on both sides; and
- Figure 12 is an axial sectional view of part of the pump for several variants.

 The centrifugal pump 1 shown in FIGS. 1 and 2 comprises a body 2 of generally circular shape with an axis 3 with a central inlet orifice 4 and a radial outlet orifice 5. This body 2 is closed, opposite to the inlet 4, by a bottom 5 having the general shape of a disc extending by an axial sleeve 6, also opposite the orifice 4, housing sealing means 7 for the passage of the shaft drive s of the impeller 9 with vanes 10 distributed regularly around the axis 3.

 The body 2 has a crown 11 of axis 3 extended, opposite the bottom 5a 'by a short central tube 12 ending in the inlet orifice 4 and on which depends a sleeve 13 for connection to a pipe. (not shown) for supplying liquid to the pump. The body 2 also has, directed towards the bottom 5a 'a rim 14 with an internal face 15 constituting a volute in the general shape of a spiral centered on the axis 3 and making it possible, as will be seen below, to direct, in combination with the wheel 9, the liquid towards the outlet orifice 5.

 The rim 14 ends with recesses 16 cooperating with complementary parts of the bottom 5a to allow the centering of this bottom relative to the body 2. A seal 17 is interposed between the body and the bottom to ensure sealing.

 A radial sleeve 18 protrudes outside the flange 14 with an opening 19 with a radial axis 20 opening on one side inside the pump body and, on the other side, towards the outlet orifice 5. This opening 19 houses a socket 21 pierced with an opening 22 also of axis 20 ending, at the outlet in the body 2, by a flared part 23, or chamfer, frustoconical with an angle at the top equal to approximately 60 , a value which is favorable for silent operation of the pump.

 From the free end of the sleeve 18 depends a flange 24 for connection to another flange 26 at the end of a tube 25 for discharging the liquid (Figure 3).

 The opening 19 has at its free end a portion 27 of larger diameter receiving a crown 28 surrounding the end of the sleeve 21. The length along the axis 20 of the crown 28 is equal to the length, along the same axis , from the part 27 of the opening 19 of the sleeve 18 so that, when the shoulder between said crown 28 and the body of the sleeve 21 rests on the shoulder 30 forming the bottom of the recess at the end of the opening 19, the end face 31 of the sleeve and the crown is coplanar with the end face 32 of the sleeve 18 and of the flange 24. A seal 33 overlaps the faces 31 and 32 and is clamped between these faces and the face 34 at the end of the flange 26 and the tube 25.

 The wheel 9 comprises a cylindrical central sleeve 40 of axis 3 with, at one end, an opening facing the inlet orifice 4; The other end of the sleeve 40 is surrounded by a crown or flange 41 (FIG. 2) separated from another similar crown 42 by the blades 101, 102, etc.

 Two neighboring blades, for example those of references 101 and 102, delimit between them a channel 43 whose cross section gradually increases from the inlet, in the vicinity of the sleeve 40, towards the outlet 45, at the periphery of the wheel.

 The shape of the internal surface 15 of the body 2 is such that the gap 46 between the periphery 47 of the wheel 9 and this surface 15 has a section increasing progressively from a shoulder 48 in the vicinity of the internal outlet of the opening 19 up to this opening, after one complete revolution in the direction of rotation f of the wheel (Figure 1). The liquid arriving at the inlet of the channel 22 of the sleeve 21 is directed towards the outlet orifice 5 thanks to the presence of the shoulder 48 and is not recycled into the pump due to the narrow width of the interval 46 beyond this shoulder.

 It will be noted that, unlike conventional centrifugal pumps, the spout 48a delimited by the shoulder 48 and the start of the surface 15 forms an obtuse angle close to a right angle.

 The sleeve 21 is removable from the sleeve 18 so that it can be replaced by a sleeve whose diameter d (FIG. 6) of its channel is different, larger or smaller. It is thus possible, as will be seen below, to modify the operating characteristics of the pump whereas until now, use was made either of a modification of the diameter of the wheel 9 or of the degree of opening of a valve downstream pump 1.

 It is important to note that the diameter d can be less than the axial width 1 (FIG. 6) of the channels 43. For example for a wheel 9 of diameter D equal to 180 mm and of width 1 of 5 mm, the diameter d can be between 3 and 12 mm.

 The variant shown in Figure 4 differs from the embodiment shown in Figure 3 in that the end face 32 of the flange 24 has a central boss 50 whose visible face 51 is coplanar with the face 31 of the crown 28. Similarly, the counter-flange 26 has a boss 52 corresponding to the boss 50.

 In the example shown in FIG. 5, the counter-flange 26 comprises a centering rib 53 centered on the axis 20 with an internal face 54 of diameter slightly greater than the outside diameter of the crown 28. This rib 53 also has a outer face 55 of diameter slightly smaller than the diameter of a recess 56, of larger diameter than the recess 27. of the opening of the sleeve 18.

 The rib 53 thus contributes, in combination with the external face of the crown 28 and the recess 56 at the end of the opening 19, to the centering of the flange 26 relative to the flange 24.

The seal 60 is interposed between the bottom of the recess 56 and the free end of the rib 53.

 The operation and the performances as well as other characteristics of the pump which have just been described will now appear with the description below made in relation to FIGS. 6 to 9.

 On the diagram of FIG. 7, the flow rate Q is plotted on the abscissa, the outlet pressure H, the power P absorbed by the pump and the parameter NPSH which is the pressure of the liquid at the inlet of the pump at the ordinates. - below which the pump is subjected to cavitation (dangerous for its constituent parts) and is defused.

The curves 61, 62, 63, 64, 65 and 66 are curves of variation of the pressure H as a function of the flow for diameters d of opening 22 of the sleeve 21 (FIG. 6) of different values, respectively dl to d6, the order relation between the diameters being as follows: dlc d2 <d3 <d4 Ud5 <d6
Curve 67 represents the variation of the power absorbed by the pump as a function of the flow rate Q.

 The curves 71 to 76 are curves of variation of the NPSH pressure as a function of the flow rate for the diameters dl to d6 respectively.

 The performance of the pump changes with the diameter d of the sleeve until they are limited by the width I of the impeller (FIG. 6). Thus, any increase in d beyond d6 "(causes no change in the characteristics of the pump beyond the dotted curve 66 in FIG. 7.

 In this example, the characteristics of the pump are such that, even for a diameter d equal to d6, the specific speed is low, at most equal to approximately 10. When the diameter d is less than d6, the specific speed is even lower because the flow rate and the outlet pressure decrease with the diameter d.

 . * The outlet pressure H at zero flow is the same, equal to Ho (figure 7), whatever the diameter d. Thus the bundle of curves 61 to 66 has, for the same diameter D of the wheel 9, a common point A with coordinates Q = O and H = Ho.

 For low values of the diameter d, the outlet pressure H varies over a wide range while the flow rate Q varies on the contrary according to a narrow range. This property makes it possible to use the pump with a relatively small diameter d of the opening 22 to regulate the pressure in the liquid circulation network connected to the pump with an almost constant flow rate.

 It can also be observed that the curve 67 of variation of the power absorbed as a function of the flow rate is independent of the value of the diameter d and that this power has a reduced value.

It is limited for a given diameter d, for example d4 according to FIG. 7, at point C on curve 67 corresponding to point B of maximum flow rate on curve 64.

 It is thus possible, provided that the diameter D of the wheel 9 is kept constant, to drive the pump 1 by a motor of useful power limited to the strict minimum without risk of overload, since the power absorbed is easily determinable. The cost of the pumping unit can thus be reduced to a minimum and the drive motor can operate at its nominal load, that is to say at optimum efficiency, the operating cost thus being as low as possible .

 When the diameter has a small value, it can be seen that the pump can be operated at a very low flow rate up to, for example, a few hundred liters per hour for pressures H of approximately 50 meters of water, at 2,900 rpm, and this in continuous operation without the generation of vibrations harmful to the service life of the pump and an annoying noise which could occur if a call was made for a valve downstream of the pump .

 The noise reduction also contributes to the chamfer 23 at the entrance to the opening 22.

 Another advantage of the method according to the invention, which consists in varying the diameter d of the outlet channel 22, is that, as can be seen on curves 71 to 76, the pressure NPSH, minimum pressure to avoid cavitation and defusing, is practically independent of the diameter d for a large part of each pressure-flow curve.

 The characteristics of the pump can be further extended by also varying the diameter D of the wheel 9. These variations in performance are illustrated in FIGS. 8 and 9.

 FIG. 8 is a diagram representing the variations as a function of the flow rate Q, plotted on the abscissa, the pressure H and the absorbed power P, plotted on the ordinate, for different values of the diameter d and of the diameter D of the wheel 9. The curves 61, 62, 63 and 64 of this FIG. 8 are identical to the curves of the same references in FIG. 7.

 The dashed lines 61 ′, 62 ′, 63 ′ and 64 ′ correspond to curves 61 to 64, respectively, with the same diameters d of the outlet channel but for a diameter D ′ of the wheel 9 less than the diameter D (wheel 9 'shown in broken lines in Figure 6). It can be observed that the pressures H and the flow rates Q are lower than the corresponding parameters for a diameter D of the wheel 9 which is higher.

 The curve 67 'corresponds to the curve 67 of absorbed power but for the diameter D'. The figure shows that the absorbed power is lower when the wheel diameter is smaller.

 FIG. 9 represents the variations of the NPSH pressure as a function of the flow Q. The curves 71 ', 72', 73 'and 74' in dashed lines represent the variations of said NPSH pressure as a function of the flow Q for the same values as the curves respectively 71, 72, 73 and 74 but for the wheel diameter D 'smaller than the diameter D.

 This figure 9 shows that this NPSH pressure has, for low flow rates, almost always the same value.

 Each of the parts of the pump body 2 is manufactured in one piece by steel or cast iron foundry. In the case of the body 2, the release is carried out at one time by the side intended to be closed by the bottom 5a I1 is not necessary to provide, for molding, of added core which would increase the manufacturing price.

 The wheel 9 is also manufactured in one piece by molding in steel, stainless or not, or in cast iron. As we saw above, it is necessary, in this case, that the width 1 is greater than 1/40 of the diameter D. The flow rate is reduced and the outlet pressure increased - hence the specific speed ns reduced by the choice the small value of the diameter d of the outlet channel. In other words, compared to the usual methods of manufacturing centrifugal pumps, the impeller is oversized, the limitation of the flow rate being obtained only by limiting the cross section of the outlet channel.

 The channel 43 having a length, in the direction of the axis 3, which is not too small, the (inevitable) irregularities of the internal faces of the flanges 41 and 42 due to molding do not reduce the performance of the pump. In addition, two pumps of the same dimensions have practically the same performance.

 In the embodiment shown in FIG. 2, to facilitate manufacturing by molding, the internal surface 15 is rectilinear in section along a plane passing through the axis 3. However, as a variant, it is possible, in order to improve the performance of the pump, to give a more complex section to this surface 15, for example those shown in FIG. 12.

 In a first embodiment, shown in solid lines in this figure 12, the surface 15 has a groove 85 whose bottom is, in section along a plane passing through the axis 3, rectilinear. In the first embodiment shown in phantom, a deeper groove 86 is provided with a bottom and curved edges, which has a radial axis 87 of symmetry. In the second variant shown in phantom, the groove 88 is asymmetrical relative to the axis 87.

In this case, it has a straight edge 89 connected by a curvature 90 to a substantially flat bottom 91. The second edge of this groove 88 is curved in the shape of an arc of a circle 92 connecting to the straight bottom 91 with another edge 93 substantially rectilinear approaching the axis 87 at an angle of about 4.jO.

 In these embodiments illustrated in Figure 12, it is necessary to provide a release core to allow the manufacture of the grooves.

 In the example of FIG. 10, the wheel 91 does not include a flange similar to the flange 41 in the embodiment shown in FIGS. 1 and 2, the blades 10 ′ thus projecting from the flange 42 ′.

This arrangement facilitates the use of the pump for liquids containing abrasive particles or fibers. The edges 95 of the blades 10 'lying in a plane transverse to the axis 3' are a short distance from the internal face 96 of the ring 11 'of the pump body in order to facilitate the' grinding of said particles.

 Such grinding is further improved with the embodiment shown in Figure 11 in which the wheel 92 is devoid of flange. In this case, the edge 95 of the blade 10 "which faces the inlet orifice is a short distance from the surface 96 and, similarly, the opposite edge 97 is a short distance from a surface 98 of a part 99 attached to the bottom 5 "of the pump body.

 Of course, it is within the scope of the invention to manufacture a series of pumps of identical dimensions, however, differing only in the section of their outlet channel so that their performance is different.

 It is also within the scope of the invention to produce the outlet channel by a simple drilling of the pump body obtained by foundry. The diameter of this channel is for example less than about 15 mm.

 Accessories constituted by a set of sockets having channels of different sections and the same external dimensions, that is to say for the same pump, also come within the scope of the invention.

 The sockets may be made of a material resistant to corrosion.

Claims (13)

 1. Centrifugal pump for single-stage liquid having a body with an inlet port and an outlet port at the end of a channel and an impeller housed in this body, characterized in that the section of the outlet channel ( 22) is limited so that the specific speed ns of the pump is at most equal to approximately 10.  2. Pump according to claim 1, characterized in that the body (2) and the impeller (9) are made of a material allowing their manufacture by foundry.  3. Pump according to claim 1 or 2, characterized in that the channels (43) formed between the blades (10) of the wheel are closed transversely to the axis (3) by flanges (41, 42) of a single piece with the rest of the wheel.  4. Pump according to claims 2 and 3, characterized in that the axial width (1) of the channels (43) between the blades (10) of the pump (1) is greater than 1/40 of the diameter (D) of the wheel (9).  5. Pump according to any one of claims 1 to 4, characterized in that the outlet channel (22) has a circular section.  6. Pump according to any ulva of claims 1 to 5, characterized in that the outlet channel (22) of the pump is formed in a socket (21) disposed in a housing (19) of the body (2) of the pump (li.  7. Pump according to claim 6, characterized in that the sleeve (21) is made of a material resistant to abrasion and / or to corrosion.  8. Pump according to claim 6 or 7, characterized in that the housing (19) of the pump body has an irregularity (27) to which corresponds an additional irregularity (28) of the sleeve (21) for immobilization of this last in the body (2).  9. Pump according to any one of claims 1 to 8, characterized in that, to penetrate into the outlet channel (22) of the pump body, the liquid performs a change of direction of about 90 "thanks to a shoulder (48) from the internal surface (15) of the body in the vicinity of the channel.  10. Pump according to any one of the preceding claims, characterized in that the outlet channel (22) of the pump body has a frustoconical inlet chamfer (23) with an angle at the apex of approximately 600.  11. Pump according to any one of the preceding claims, characterized in that the internal part of the body is shaped to be able to be produced by molding without using a core.  12. Pump according to any one of the preceding claims, characterized in that the transverse dimension (d) of the outlet channel (22) is at most equal to the width (1), along the axis of rotation, offered for passage liquid between the blades (10) of the wheel (9).  13. Set of sockets, characterized in that each of them being intended for a pump according to claim 6 and having all the same shape and the same external dimensions, two sockets of the same set are distinguished by the section of their channel .